1. Field of the Invention
The present invention generally relates to optical communications, and a method for reducing the number of pins on a physical layer device, such as an Ethernet device in an optical transceiver.
2. Background Art
High speed data links transmit data from one location to another over transmission lines. Optical data links are one type of high speed data link. In an Ethernet based optical data link, each link partner typically includes a fiber module transceiver that transmits and receives laser light. The fiber transceiver is also coupled to an Ethernet physical layer transceiver that processes the electrical signals sent to, and received from, the optical fiber module.
FIG. 1 illustrates a conventional link partner configuration for an Ethernet-based optical data link. Each link partner includes an Ethernet physical layer (PHY) 102 that transmits and receives electrical signals with a optical fiber transceiver module 106 (also called an “optical fiber module” or a fiber module, for short). The optical fiber module 106 converts the electrical signals from the Ethernet PHY 102 to optical data signals that are transmitted over an optical link to another link partner (not shown) via the optical port 114. Likewise, the fiber module 106 also receives optical data signals at the optical port 114 and converts these optical data signals to electrical signals that are sent to the Ethernet PHY 102. Between the Ethernet PHY 102 and the fiber module 106, each link partner includes a transmit termination 100, a receive termination 107, and a signal detect termination 112 that are discussed further below.
The transmit termination 100 of the Ethernet PHY includes a matching network 104, and two transmit pins 103a and 103b on the Ethernet PHY 102 that correspond to transmit pins TR on the fiber module 106. The receive termination 107 of the Ethernet PHY 102 includes a matching network 110, and two receive pins 108a and 108b on the Ethernet PHY 102 that correspond to receive pins RX on the fiber module 106. The signal detect termination 112 includes the Ethernet PHY 102 and the fiber module 106 and two signal detect pins 110 that correspond to signal detect pin SD on the fiber module 106.
During operation, the fiber module 106 sends a signal to the signal detect pins 110 to indicate the receipt of valid optical data. This is necessary because low power optical data signals can cause invalid electrical data to be sent to the Ethernet transceiver 102. The fiber module 106 de-asserts the signal detect 110 when the light input power decreases below a certain level (e.g. the fiber cable is removed or sliced). Vice versa, the signal detect 110 is asserted when the light input power increases above a certain level. The link on a 100Base-FX chip is a function of the signal detect input. When the signal detect is asserted, the link will be up and when the signal detect is de-asserted the link is down.
The separate signal detection (e.g. pins 110) on the Ethernet PHY 102 is utilized in the conventional system because invalid data can transmitted from the fiber module 106 to the receive pins 108. Therefore, the signal detect 110 is used to notify the Ethernet PHY 102 when the data should be recognized. For instance, a signal high on the signal detect lines should be used to indicate that data should be received and processed. A signal low indicates data should be ignored.
The transmit pins 103, the receive pins 108, and the signal detect pins 110 are implemented on a common substrate of the Ethernet transceiver 102, and are needed for each port of a multi-port Ethernet chip. Since substrate area is limited, the number pins becomes a limiting factor in determining how many channels can be serviced by an Ethernet PHY 102.
Therefore, what is needed is an apparatus and method for implementing and operating an optical transceiver that reduces the number of pins needed for each port.